The Arab Spring uprisings have given al-Qaeda new arenas in which to rebuild, increasing the chances of home-grown terrorist attacks in Britain, the head of its domestic intelligence has warned.
Instability in the region had created "a permissive environment for al-Qaeda", Jonathan Evans, director general of MI5 said in a lecture on London this morning NZ time.
There was was evidence British "would-be jihadis" were travelling in search of training and opportunities for militant activity, he added.
"Some will return to the UK and pose a threat here," he said. "This is a new and worrying development and could get worse as events unfold.
"We will have to manage the short-term risks if there is to be a longer-term reward from the Arab Spring," he added.
Al-Qaeda's influence was shifting away from Afghanistan and Pakistan and towards Yemen, Somalia and the Sahel, said Evans.
"We appear to be moving from a period of deep and focused threat to one where the threat is less monolithic but wider," he added.
In 2005, four home-grown militants killed 52 people in a coordinated suicide attacks on London's transport system.
With London hosting the Olympic Games in July and August, security has become an increasingly important issue in Britain.
Evans acknowledged that the Games offered "an attractive target for our enemies", but backed the security forces to ensure a safe event.
"The Games are not an easy target and the fact that we have disrupted multiple terrorist plots here and abroad in recent years demonstrates that the UK as a whole is not an easy target for terrorism," he said.